ELECTRICAL CHARACTERISTICS OF LOW VOLTAGE ...

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TIA PN-4584 Revision 1.2 4.4 System parameters 4.4.1 Multiple receiver operation (Figure 18 and Figure 19) The generator has the capability to furnish the DC signal necessary to drive multiple (up to 32) parallel connected receivers (without internal termination). However, the physical arrangement of the multiple receivers involves consideration of stub line lengths, location of the termination resistor, number of receivers, data signaling rate, circuit common, etc., that may degrade dynamic characteristics of the signal at the receivers if not properly implemented. It is recommended that stub lengths off the main line be as short as possible. In general, the propagation delay of the stub, should not exceed 30% of the signal transition time to prevent reflections and a severe impedance discontinuity. For applications with receivers without internal termination, the external termination resistor must be located at the far end (last receiver) of the interconnect. G Stub Length R1 ZT R2 Figure 18 - Multiple receiver operation - multidrop application NOTE - If the configuration illustrated in Figure 18 is employed, only the receiver at the far end of the cable may be a terminating receiver. All receivers located between the generator and the final receiver must be nonterminating receiver(s). Multiple terminating receivers would present a low impedance load to the generator which would violate the total load limit (see 4.4.3), and adversely attenuate the signal. The configuration shown in Figure 19 is composed of two independent uncomplicated point-to-point applications. At the expense of the second balanced interconnecting media, and termination impedance, the problem of stub lengths is eliminated, along with any impedance discontinuities that mid balanced interconnecting media connectors, and stubs may present. Signal quality is superior in an uncomplicated point-to-point configuration over a multidrop configuration. At the highest speeds it may not be possible to meet the 30% recommendation. In this case, a point-to-point configuration is recommended. 20 of 31
TIA PN-4584 Revision 1.2 G ZT R G ZT R Figure 19 - Uncomplicated point-to-point application 4.4.2 Failsafe operation Other standards and specifications using the electrical characteristics of the LVDS interface circuit may require that specific interchange circuits be made failsafe to certain fault conditions. Such fault conditions may include one or more of the following: 1) generator in power-off condition 2) receiver not connected with the generator 3) open-circuited interconnecting cable 4) short-circuited interconnecting cable 5) input signal to the load remaining within the transition region (±100 mV) for an abnormal period of time (application dependent) When detection of one or more of the above fault conditions is required by specified applications, additional provisions are required in the load and the following items must be determined and specified: 1) which interchange circuits require fault detection 2) what faults must be detected 3) what action must be taken when a fault is detected; the binary state that the receiver assumes 4) what is done does not violate this Standard The method of detection of fault conditions is application dependent and is therefore not further specified as it is beyond the scope of this Standard. 4.4.3 Total load limit The total load (ZL) including multiple receivers, failsafe provisions, and media termination shall have a total resistance greater than or equal to 90 Ω and less or equal to 132 Ω between its input points A' and B', shown in Figure 2. The receiver(s) shall not require a differential input voltage of more than 100 mV in magnitude for all receiver(s) to assume the intended binary state. 90 Ω ≤ ZL ≤ 132 Ω 21 of 31
Page 1: TIA PN-4584 Revision 1.2 ELECTRICAL
Page 4 and 5: TIA PN-4584 Revision 1.2 4.2 Load c
Page 6 and 7: TIA PN-4584 Revision 1.2 FOREWORD (
Page 8 and 9: TIA PN-4584 Revision 1.2 2 DEFINITI
Page 10 and 11: TIA PN-4584 Revision 1.2 3.2 Data s
Page 12 and 13: TIA PN-4584 Revision 1.2 4.1 Genera
Page 14 and 15: TIA PN-4584 Revision 1.2 4.1.2 Offs
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Page 18 and 19: TIA PN-4584 Revision 1.2 4.2 Load c
Page 20 and 21: TIA PN-4584 Revision 1.2 4.2.3 Term
Page 22 and 23: TIA PN-4584 Revision 1.2 4.2.4 Rece
Page 24 and 25: TIA PN-4584 Revision 1.2 NOTE - Due
Page 28 and 29: TIA PN-4584 Revision 1.2 5 ENVIRONM
Page 30 and 31: TIA PN-4584 Revision 1.2 Optional S
Page 32 and 33: TIA PN-4584 Revision 1.2 A.1.2 Typi
Page 34 and 35: TIA PN-4584 Revision 1.2 A.2 Cable
Page 36 and 37: TIA PN-4584 Revision 1.2 SWITCHING

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